Process for producing nano-powders and poeders of nano-particles loose aggregate

ABSTRACT

The present invention discloses a process for producing nano-powders and powders of nano-particle loose aggregate, which comprises: (a) providing at least two-reactant solutions A and B capable of rapidly reacting to form deposits; (b) supplying the at least two solutions A and B at least at the reaction temperature into a fixing and reaction precipitator respectively, in which mixing reaction and precipitation are continuously carried out in sequence, the said mixing and reaction precipitator being selected from at least one of a tubular ejector mixing reactor, a tubular static mixing reactor and an atomizing mixing reactor; and (c) treating the deposit-containing slurry continuously discharged from the mixing reaction precipitator. The process makes it possible to control the size of the nano-particles, produces particles uniform in size, good in dispersibility and high in yield, while being simple and saving energy. The process can be used to produce nano-powders of nano-particle aggregates of various kind of metals, oxides, hydroxides, salts, phosphor compounds, sulphur compounds, organic compounds, and inorganic organic compounds.

FIELD OF THE INVENTION

[0001] The present invention relates to a method of preparation forultra fine powders. More specifically, it relates to a method ofpreparation for nanometer grade powders (hereinafter called asnano-powders) and powder of loose aggregates of the nanometer gradeparticles (hereinafter it is called as nano-particle loose aggregatepowder, and the nanometer grade particle as nano-particle). Especially,it relates to a method utilizing liquid phase chemical reaction to forma precipitate to prepare nano-powders and nano-particle loose aggregatepowders.

BACKGROUND OF THE INVENTION

[0002] It is well known that particulates of metals or metal oxides withsizes at nanometer level or submicron level are very useful industrialproducts in many fields of application. These applications include themanufacture of catalysts used in chemical industry, pottery andporcelain, electronic elements, coating, capacitor, mechanical-chemicalpolishing slurry, magnetic tape and fillers for plastics, paint orcosmetics.

[0003] It is possible to produce ultra fine particulates of metals ormetal oxides by various technologies including high temperature gasphase method, mechanical method, chemical method and etc. Reviews on thegeneral technology of the production of nano-particle were published inthe following papers: V. Hlavacek and J. A. Puszynski, “Advances in theChemical Industry of Advanced Ceramics”, Industrial Engineering andChemistry Research, 1996, vol. 35, 349-377; “Advances on the Method ofPreparation for Nano-particles”, Chemistry Bulletin (in Chinese), 1996,No. 3, 1-4. In CN 1217387A, there was also a detailed discussion on theadvantages and disadvantages of the various technologies.

[0004] The process of the liquid phase precipitation method is simple.When compared with the gas phase method, solid phase method or otherliquid phase method, its controlling condition is not so critical andits cost is lower. Therefore nowadays the liquid phase precipitationmethod is widely used.

[0005] The characteristics of the process of the conventional liquidphase precipitation method are as follows: stirring pot is used to carryout mixing reaction, and at least one of the reactant solutions isgradually added into the stirring pot by dropping, flowing in oratomizing for a relatively long time. Although this technology forpreparing nano-particles has the advantage of simple operation, low costand high yield, it has three generally recognized disadvantages asfollows: (1) it is difficult to control particle diameter; (2) it isdifficult to obtain very small particle diameter; (3) it is difficult toeliminate hard agglomeration among particulates. The origin of thedrawbacks of the pot technology comes from the too long feeding time forone of the reactant solution and from the mixing of the reaction,product and precipitate formed at different stages of time whilestirring. Nuclei formed at the initial stage will undergo growth andcollision coalescence among small particulates to form nano-particles.Due to long time, nano-particles will grow to be relatively larger insize and will agglomerate together among nano-particles. Theparticipation of the product formed in the later stages will induceagglomeration hardening. As mentioned above, these are the causes of theabove-mentioned three drawbacks of the large pot technology in preparingnano-powder.

[0006] Therefore, various processes of liquid phase precipitation methodfor producing nano-powder without the use of stirring pot have beensuccessively developed. Patent Application No. SE 99/01881 disclosed thefollowing method and facilities: on the basis of a stream of carrierfluid flowing continuously in a pipe, two kinds of reactant solutionswere injected in the form of periodical, intermittent pulse into thepipe at the same location. The reaction zone where the mixing of theinjected two reactant solutions took place was separated in the carrierfluid. The lasting time for the course of mixing, reacting, and formingprecipitate was very short. The invention claimed that the quality ofthe nano-particles was very good, with particulate size at 10-20 nm,slight inter-particulate agglomeration or even no agglomeration. Thedrawbacks of that method are: (1) reactant solutions are injected in apulse mode and the mixing process is not continuous, thus the process isnot favorable for large-scale continuous industrial production, andsince carrier fluid must be used, the manufacturing process getscomplex, it not only consumes carrier fluid but also needs a separationtreatment for the carrier fluid and etc. and thus increases theproduction cost; (2) the method does not take any effective measures toreinforce and to adjust the mechanical mixing efficiencies of the tworeactant solutions, therefore, it is impossible to effectively controlthe mechanical mixing efficiency of the reactant solutions. The abovetwo drawbacks both shall be improved.

[0007] Other 2 papers, “Preparation of Strontium Carbonate Nano-powderby Liquid-Liquid Method in Rotating Packed Bed”, Science and Technologyin Chemical Industry (in Chinese), 1999, 7(4) 11-14 and “ExperimentalStudy on Microscopic Mixing in Rotating Packed Bed”, Chemical ReactionEngineering and Technology (in Chinese), 1999, 9, Vol.15, No. 3,328-332, described another kind of continuous process without the use ofstirring pot. Two reactant solutions were allowed to pass continuouslythrough rotating packed bed at one time. In the rotating packed bed, tworeactant solutions mixed, reacted, formed nuclei and formednano-particles. The paper stated that under the action of super gravity,the reactant solutions passed through the rotating packed bed and weredispersed, broken by the packing and formed very large and continuouslyrefreshing surface area, greatly reinforced the material transfercondition. Besides, the process of rotating packed bed has the advantageof high intensity of fluid passage and short resident time. However,there were still some drawbacks in the method of super gravity rotatingpacked bed. Due to the high compactness of the fillers such as steelwire net and in the packed bed, what obtained by the solution was notthe action of stirring and shear. When solution entered into the packedbed, it as a whole rotated with the packed bed and obtained centrifugalforce. Under the action of centrifugal force, the solution would flowfrom inner fringe of the rotor to outer fringe along the interstitialsof the packing and in the course of this process, mixing of solutiontook place. The mechanical mixing intensity and the adjustingsensitivity of such kind of mixing were not high enough and thus theperformance of the preparation of nano-powder was not ideal. Exceptnano-powder of CaCO₃ and SrCO₃, no report on the successful preparationof important species such as Zro₂, TiO₂ by using rotating packed bed wasdisclosed. Therefore the method seems to need further improvements.

[0008] As mentioned above, a good mixing and reacting facility forcontinuous passage of two reactant solutions should have thecharacteristics of high mechanical mixing intensity, adjustablemechanical mixing intensity and simplicity of structure. Within suchfacility, the solution should acquire vigorous stirring, shearing andturbulence and would quickly be separated and broken into isolated verysmall sized micro liquid agglomerates in order to enlarge the interfaceof the two solutions so as to provide good conditions for the processesof molecular diffusion, chemical reaction, nucleation and etc.

[0009] Chinese Patent Application No.01106279.7 filed on Mar. 7, 2001,which has not been disclosed and is entirely incorporated herein as areference, provides a process without using a stirring pot comprising:continuously feeding reactant solutions into a dynamic rapidly andorderly micro liquid agglomerate mixing and reacting precipitator toseparate the reactant solutions into a large amount of micro liquidagglomerates capable of rapidly mixing and reacting with each other in aturbulence state in reaction zones orderly arranged along the fluiddirection to from a precipitate-containing slurry; feeding theprecipitate-containing slurry from the mixing and reacting precipitatorto a procedure of rinsing and filtering; and treating the resultingprecipitates by various processes such as drying, heat treatment,pulverization and the like. The nano-particle is very fine and uniform.The hard agglomeration among the nano-particles is prevented.

[0010] Therefore, the objective of the present invention is to furtherimprove the process disclosed in Chinese Patent Application No.01106279.7 and to provide a further method of preparing nano-powder byliquid phase precipitation. The method of the present invention adopts amixing facility which is simple in structure, can provide high andadjustable mechanical mixing intensity and can be used for large-scaleproduction of good quality nano-powder. The method is widely applicablein the production of nano-powders of oxides, hydroxides, salts, metalsand the like. Moreover, the number of devices can be decreased and theparameters to be controlled can be simplified.

[0011] After reading the following descriptions, this and furtherobjectives, advantages and features of the present invention will becomeclearer.

SUMMARY OF THE INVENTION

[0012] The present invention provides a method for preparingnano-powders and nano-particle loose aggregate powder, comprising thefollowing steps:

[0013] (a) providing at least two reactant solutions A and B which canreact with each other quickly to form precipitate;

[0014] (b) feeding the at least two reactant solutions A and B to amixing and reaction precipitator separately which is at least oneselected from a group consisting of tubular ejection mixing reactor,tubular static mixing reactor and atomization mixing reactor at atemperature not lower than the reaction temperature for continuous andorderly mixing, reaction and precipitation, where the at least tworeactant solutions A and B react with each other in a form ofmicro-liquid aggregate and form a precipitate-containing slurry; and

[0015] (c) post-treating the precipitate-containing slurry dischargedcontinuously and orderly from the reaction precipitator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic diagram for the spatial concentrationdistribution vs. time.

[0017]FIG. 2 is the process flow diagram for a method of the presentinvention.

[0018]FIG. 3-a shows a coaxial ejection mixing reactor.

[0019]FIG. 4-a shows an ejection mixing reactor with an inlet at a sidethereof.

[0020]FIG. 3-b, 3-c and FIG. 4-b, 4-c show an ejection mixing reactorfor three solutions.

[0021]FIG. 5-a, 5-b show a coaxial ejection mixing reactor with aplurality of nozzles through which the solution A is ejected and aninlet through which the solution B flows.

[0022]FIG. 5-c, 5-d show a coaxial ejection mixing reactor with aplurality of nozzles through which the solution A are ejected and aplurality of nozzles through which the solution B are ejected.

[0023]FIG. 6 shows a coaxial ejection mixing reactor with an side inletthrough which the solution B flows and a plurality of nozzles throughwhich the solution A and the solution C are ejected.

[0024]FIG. 7-a shows a tubular static mixing reactor for solution A andsolution B.

[0025]FIG. 7-b, 7-c show a tubular static mixing reactor for solution A,solution B and solution C.

[0026]FIG. 8-a shows a hole/separator mixing member.

[0027]FIG. 8-b shows a grid mixing member.

[0028]FIG. 9 shows an atomization mixing reactor.

[0029]FIG. 10 shows an electronic micrograph of the powder obtained inexample 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0030] In the context of the present invention, the term “nano-powder”represents a powder comprised of nano-particles having an averageparticle diameter of less than 100 nm. The excellent nano-powderobtained by the present process shall has the following advantages: asmall average particle diameter (less than 30 nm or even as low as 10nm); a narrow particle size distribution; a good dispersibility (onlysoft-linkage or slight linkage and no hard-linkage).

[0031] Herein, the term “nano-particle loose aggregate powder” means anaggregate of nano-particles linked in such a way that the nano-particlesare net-like linked and loosely dispersed in a space. A goodnano-particle loose aggregate powder shall has the following features:(1) the nano-particles have a small average particle diameter and anarrow particle size distribution; (2) the nano-particles are looselyand net-like dispersed in a space and can have a suitable strength aftera suitable aging treatment; (3) it has a high specific surface area andthus can be used as a carrier for catalysts or drugs; and (4) thedesired particle diameter thereof can be predetermined according to thegranulation and pulverization processes.

[0032] At least two different liquid fluids are separated and dispersedstepwisely to form dispersed and separated liquid micro aggregate ofsmall size by the impact, shearing, stretching and eddying functions ofa convective movement and a turbulent movement resulting from varioushigh intensity mechanical mixing. The average size of the liquid microaggregate are in relation to the way and intensity of the mechanicalmixing, and can be as small as 100 μm, tens of μm or even ten somethingof μm, see Chemical Engineering Handbook, Beijing, Chemical IndustryPublishing House, Vol. 5, p9-10. Herein, the term “micro liquidaggregate” has the above meaning.

[0033] The term “tubular ejection mixing reactor” represents a tubularejecting mixer where the reaction and precipitation will automaticallytake place following the mixing of the solutions. During the ejectionmixing, a liquid stream moving quickly (a ejecting flow or a firstliquid) is ejected into a liquid stream moving slowly (a main flow or asecond liquid). On the boundary of the ejecting flow, a mixing layer isformed due to the difference between the speed of the ejecting flow andthat of the main flow and due to the turbulent function. The mixinglayer expands along the flow direction of the ejecting flow, and allowsthe main flow to enter into the ejecting flow by carrying and mixing.The tubular ejector is a continuous flow apparatus of a high speed. Thecoaxial ejecting mixer and the ejecting mixer with a side inlet are twocommon ones. As shown in FIG. 3-a, in the coaxial ejecting mixer, thesecond liquid streams in a large diameter pipe but is not ejected intothe coaxial ejecting mixer, and the ejecting flow is ejected into thecoaxial ejecting mixer through a small diameter pipe and is coaxiallyplaced in the large diameter pipe. In the ejecting mixer with a sideinlet, as shown in FIG. 4-a, the second liquid also flows in a largediameter pipe but the ejecting flow is ejected through a small diameterpipe perpendicular to the large diameter pipe into the ejecting mixerwith a side inlet.

[0034] As a tubular ejecting mixer, a coaxial mixer with a plurality ofnozzles can be provided. For example, FIG. 5-a shows one mixer intowhich the ejecting flow B is ejected through nozzles, and FIG. 5-bfurther shows that the reactant solutions A and B are both ejectedthrough a plurality of nozzles into a large diameter pipe.

[0035] The term “tubular static mixing reactor” means a mixer withoutmovement and is a on-line mixing apparatus comprised of a serial ofmixing members placed in a pipe where the solutions will automaticallyreact and precipitate after mixing. As shown in FIG. 7, various mixingmembers can be obtained from various manufactures and are static duringthe mixing procedure. The energy for mixing comes from the additionalpressure decrease created by the flow of the solutions over the mixingmembers. Therefore, the required energy for pumping these solutions ishigher than usual. The desired number of mixing members for variousapplications depends upon the difficulty of mixing. Therefore, the moredifficult the mixing is, the more the mixing members are required.

[0036] The mixing in the static mixer includes a laminar flow mixing anda turbulent flow mixing. The laminar flow mixing is carried out by acombination of stream separating and changing of flowing direction. Butthe turbulent mixing is carried out by controlling the flux and creatingby the mixing members more intensive turbulent function higher than thatin an empty pipe. The static mixer has been widely used in processes,such as, mixing, reaction, dispersion, heat-conduction and masstransfer. The static mixer is generally operated by using a turbulentflow which can result in the breaking up of liquid aggregates due to theshear stress in the system and thus can create a bigger interface areaof liquid aggregate required for the mass transfer. The stress is inrelation to the pressure decrease. Therefore, the stress is also inrelation to the flux of the fluid through the mixer. In order to obtaina smaller micro liquid aggregate, the flux of the fluid must beincreased because singly increasing the number of the mixing members ishelpless for the system. For the mixing and dispersion, the on-linestatic mixer has such an advantage that it can be continuously operatedand requires a smaller working space. The conventional static mixer canbe arranged in a pipe of a diameter from 1 cm to 0.5 m.

[0037] The term “atomization mixing reactor” represents a novelatomizing mixer capable of transforming a reactant solution into anatomized gas stream and where the reactant solutions can automaticallyreact and precipitate after mixing. FIG. 9 shows a preferred example ofthe atomization mixing reactor at least comprising an atomizer 1 and anatomizer 2 adjacent to each other and capable of transforming thereactant solutions into oriented atomized gas streams flowing in thesubstantially same direction. The two atomizers have the same structureand characteristics and are adjusted to allow nearly all the finedroplets carried by the two atomized gas stream to fall on the sameportion of one side of roller 3 (or on the same portion of the transferbelt). Two kinds of fine droplets falling on the same portion are mixedby alternatively overlaying each other, and a slurry layer is formed.The atomizing is carried out continuously. The roller rotates slowly.The thickness of the slurry layer, obtained by mixing and reacting themicro liquid aggregates of the two solutions, can be controlled byadjusting the rotate speed of the roller. The precipitate-containingslurry is transferred by the roller or the transfer belt to scraper 4where it is scraped and collected to a funnel 5 and then transferred torinsing and filtering devices through a pipe and pump 6. The abovetransfer belt includes a wet filter cloth of a belt-type filter. Theaging time before filtering and rinsing is adjusted by controlling themoving speed of the filter cloth v and the length of the filter clothAlbefore reaching the filtering and rinsing zone. The aging time can becalculated on the basis of the formula Δt=Δ1/v.

[0038] Although not intend to be limited by any theory, it should bepointed out that the present inventor puts forward the present technicalsolution on the basis of inventor's theory integrated with experimentalresults. It should be pointed out that the following theory is used onlyto explain the present invention but not to limit the present inventionin any way.

[0039] It can be drawn from the experimental observation and mechanismanalysis that when two reactant solutions capable of reacting rapidly toform a precipitate meet together, a large amount of nuclei will beexplosively formed at the fresh interfaces of the two solutions. Afterthe explosive nuclei formation, new nuclei will no longer be formed atthat place. Let the solutions of A and B be represented by α and β, theequation of reaction will be

α+β=γ+δ, γ→precipitate

[0040] The concentration of α, β and the precipitated component γ areC1, C2, and C, respectively. FIG. 1(a) and (b) indicate the spatialdistribution curves for C1, C2 and C at time interval of t=0 and t=trespectively. When C exceeds critical nucleation concentration Ck,nucleation can take place within the region of a and b. FIG. 1(c)indicates the curve of change of concentration against time in thecourse of explosive nucleation within the region a-b. The curve is justthe known “lamer” profile. It is shown in FIG. 1(c) that after explosivenucleation, the precipitated components formed by reaction and diffusioncan only afford the growth of the nuclei already formed. New nuclei willno longer be formed because the concentration is lower than the criticalnucleation concentration. Based on the above result, the followingdeduction can be drawn. When reactant solutions A and B are intermingledrapidly in the form of micro liquid agglomerates, the following resultscan be obtained: (1) fresh interfaces of huge surface area are rapidlyformed between a definite amount of reactant solutions A and B and thena large amount of pristine nuclei will be explosively formed; thesmaller the size of micro liquid agglomerate is, the larger the surfacearea of fresh interface will be, the larger the total number of formedpristine nuclei will be, and the larger the average density (number ofpristine nuclei per unit of space) will be; (2) when the size of themicro liquid agglomerate is decreased, the time of the whole process ofmolecular diffusion and chemical reaction will correspondingly beshortened. Rapid mixing of micro liquid agglomerates and the explosiveformation of all the pristine nuclei will provide good conditions forthe simultaneity of the collision coalescence of small particulate toform nano-particles, homogeneity of particulate size as well as thedecrease of particulate dimension.

[0041] It was shown by examples that the particle size of thenano-particle formed by collision and aggregation will become smaller ifthe pristine nuclei are formed explosively and the average densitythereof is very high. At this case, vast quantities of nano-particleswill be formed and loosely fulfill the entire space in a very shorttime. Only the pristine nuclei very near the nano-particle can collidewith and enter into the nano-particle in a very short time for diffusionand migration. Therefore, the total number of the pristine nucleicolliding with and entering into the nano-particle is very small and theformed final nano-particle is of a very small particle size.

[0042] Therefore the present invention provides a method of preparing anano-powder and a nano-particle loose aggregate powder comprising thefollowing steps:

[0043] (a) providing at least two reactant solutions A and B capable ofrapidly reacting with each other to form a precipitate;

[0044] (b) at a temperature not lower than the reaction temperature,continuously and respectively feeding the at least two reactantsolutions A and B into a mixing and reacting precipitator selected froma group consisting of a tubular ejection mixing reactor, a tubularstatic mixing reactor and an atomization mixing reactor where mixing,reaction and precipitation can be continuously and orderly carried outto form a precipitate-containing slurry; and

[0045] (c) post-treating the precipitate-containing slurry dischargedcontinuously from the mixing and reacting precipitator.

[0046] As one preferred embodiment of the present invention, the methodfor preparing a nano-powder and a nano-particle loose aggregate powdercomprises the following steps:

[0047] (a) providing reactant solutions A and B capable of rapidlyreacting to form a precipitate and optionally containing an auxiliaryreacting agent and a dispersing agent, and optionally providing one ormore auxiliary reacting solutions containing at least one selected froma group consisting of a dispersing agent, an auxiliary reacting agentand a pH value adjusting agent;

[0048] (b) at a temperature not lower than the reaction temperature,continuously feeding the solutions into a tubular ejection mixingreactor or a tubular static mixing reactor where the solutions arecontinuously passed, orderly and quickly mixing and reacting with eachother to form within 0.1-120 seconds a precipitate-containing slurrywhich will be continuously discharged from the tubular ejection mixingreactor or the tubular static mixing reactor; and

[0049] (c) post-treating the precipitate-containing slurry continuouslydischarged from the tubular ejection mixing reactor or the tubularstatic mixing reactor.

[0050] As another preferred embodiment of the present invention, themethod of preparing a nano-powder and a nano-particle loose aggregatepowder comprises the following steps:

[0051] (a) providing reactant solutions A and B capable of rapidlyreacting to form a precipitate and optionally containing an auxiliaryreacting agent and a dispersing agent, and optionally providing one ormore auxiliary reacting solutions containing at least one selected froma group consisting of a dispersing agent, an auxiliary reacting agentand a pH value adjusting agent;

[0052] (b) at a temperature not lower than the reaction temperature,continuously feeding the solutions into an atomization mixing reactorwhere the solutions are atomized into atomized droplets and sprayed byan atomizer onto a transfer belt or the wall of a roller on which theatomized droplets are orderly, quickly and alternatively mixing andreacting with each other to form within 0.1-120 seconds aprecipitate-containing slurry which will be continuously discharged fromthe atomization mixing reactor; and

[0053] (c) post-treating the precipitate-containing slurry continuouslydischarged from the atomization mixing reactor.

[0054] As one specific embodiment of the present method shown by FIG. 2,reactant solutions A and B are respectively stored in a storing tank andfed through a metering pump or a flow meter into a mixing and reactingprecipitator where they can continuously, orderly and quickly mixing andreacting with each other to form a precipitate-containing slurry. Theprecipitate-containing slurry discharged from the mixing and reactingprecipitator enters into an aging (if any), rinsing and filteringprocedure, and then is dried, heat-treated, pulverized or granulated andfinally packaged.

[0055] The form of reactant solutions A and B has no specificlimitations. They can each independently be aqueous solution (includingpure water) or organic solvent solution (including liquid state purematerial). The auxiliary reacting solution can be either aqueoussolution or organic solvent solution. Reactant solutions A and B canalso contain an auxiliary reacting agent and a dispersing agent. Themixing volume ratio for reactant solutions A and B can be arbitrary, butpreferably 1:1. The mixing volume ratio for other adjuvant reactantsolutions can be arbitrary. The temperature of the reactant solutionentering the mixing and reacting precipitator can be any temperaturesufficient for carrying out the mixing and reaction. For the reactantaqueous solutions, the preferred temperature range is between 15° C. andthe boiling point of the solutions, for example, 15-98° C. For thereactant organic solvent solutions, the preferred temperature range isalso from 15° C. to the boiling point of these solutions.

[0056] There is no limitation on the dispersing agent, auxiliaryreacting agent and pH adjuster used in step (a). They can be those ofthe conventional type. The dispersing agent for the reactant aqueoussolution includes a lower alcohol and a surfactant. The sulfuric acidH₂SO₄ added into Ti(SO₄)₂ solution to inhibit hydrolysis can be taken asan example of the auxiliary reacting agent.

[0057] In step (b), the reactant solutions A and B are dispersed andbroken into many separated micro liquid agglomerates, and freshinterfaces of huge surface area are produced between the two solutions.In the vicinity of these interfaces, a huge number of pristine nucleiwill explosively be formed along with the occurrence of moleculardiffusion and chemical reaction. Reactant solutions A and B areintermingled in the form of micro liquid agglomerates, which will resultin the great shortening of the time necessary for the process of themolecular diffusion and chemical reaction.

[0058] According to one preferred embodiment, when the residence time ofthe solutions through the “mixing and reacting precipitator” is longerthan the time of diffusion and reaction, the particle diameter of thenano-particle can be decreased, and the hard agglomeration among thenano-particles can be lessened or even eliminated by shortening saidresidence time to 0.2-10 seconds.

[0059] In the step (c) of the present invention, theprecipitate-containing slurry continuously discharged from the mixingand reacting precipitator enters into a rinsing and filtering procedureto prepare a nano-powder or into an aging, rinsing and filteringprocedure to prepare a nano-particle loose aggregate powder. The agingtime is 0-120 min. If no aging is required or the aging time is shorterthan 20 minutes, the devices capable of being continuously operated arepreferred. The type of washing can include ionic electric fielddialysis, water or organic solvent washing and etc.

[0060] The post-treatment can further include drying, heat treatment,pulverizing or granulating, and final packaging. The examples of dryingprocesses include conventional drying, spray drying, vacuum drying,freeze drying, supercritical drying and azeotropic distillation. Thepreferred temperature for heat treatment is in the range of 200-1000° C.

[0061] The amount and running order of the above-mentionedpost-treatment steps can be adjusted according to the types of theproduct and detailed request of the customer.

[0062] The mixing and reacting precipitator used in step (b) of thepresent invention will be specifically described in reference to theattached figures.

[0063] The examples of the tubular ejection mixing reactor include acoaxial ejection mixing reactor, an ejection mixing reactor with sideinlets and an ejection mixing reactor with a plurality of nozzles.

[0064]FIG. 3-a shows a coaxial ejection mixing reactor used for reactantsolutions A and B, which includes an ejecting inlet 1 for one solution(called as the ejected solution), an inlet 2 for another solution(called as the second solution), and a mixing and reacting zone 3comprised of pipe(s) having a bigger diameter. The second solutionenters into the reactor from the inlet 2, flows as a turbulent flow inthe large diameter pipe at a slower speed. The ejected solution isejected at a high speed through the inlet 1 of a small diameter pipecoaxial to the large diameter pipe. During the ejecting process, amixing layer is formed due to the function of turbulent flow and thespeed difference between the ejected solution and the second solution.As a result, the second solution enters into the ejected solution, andtwo solutions are broken and dispersed into separated micro liquidaggregates due to impacting, shearing, stretching and eddying. Theaverage size of the micro liquid aggregate is in relation to the mixingintensity and reynolds number Re, specifically, to the pipe diameter andflow speed. The flow speed is in relation to the flux and the pressure.The average size of the micro liquid aggregate can be as small as tensof microns or even just 10-20 microns. As previously stated, a largeamount of pristine nuclei will be explosively formed in the vicinity offresh interfaces of the two solutions. The density (number of pristinenuclei per unit of volume of the reactor) is relatively high. As shownby some experiments, the particle size of the nano-particle produced bycollision and aggregation between the pristine nuclei will becomesmaller and even as small as several nanometers. The nano-particles areloosely distributed in the space.

[0065]FIG. 4-b shows an ejection mixing reactor with side inlets forreactant solutions A and B. One solution (called as the second solution)enters through inlet 2 into and slowly flows as a turbulent flow in alarge diameter pipe. Another solution (called as the ejected solution)is ejected into the ejection mixing reactor through an inlet 1 at theend of a small diameter pipe perpendicular to the large diameter pipe.The ejected solution and the second solution mix and react with eachother in a mixing and reacting zone 3 to form a precipitate. Theprinciple and the control of this reactor is substantially identical tothose of the coaxial ejection mixing reactor.

[0066]FIG. 3-b, FIG. 3-c, FIG. 4-b, and FIG. 4-c show an ejection mixingreactor for three solutions A, B and C. Besides the members shown inFIG.-a and FIG. 4-a, this reactor further comprises an inlet 4 for anadjuvant reactant solution C. Preferably, the adjuvant reactant solutionC is ejected into the reactor through inlet 4 so as to homogeneously mixwith other solutions.

[0067]FIG. 5-a, 5-b show a coaxial ejection mixing reactor with aplurality of nozzles as small diameter pipes for solution A and a sideinlet for solution B. The reactor further has a large diameter pipe. Thelarge diameter pipe and the small diameter pipes are arranged at thesame direction. Solution A is ejected into the reactor through theplurality of nozzles and solution B flows into the large diameter pipethrough a side inlet.

[0068]FIG. 5-c, 5-d show a coaxial ejection mixing reactor with aplurality of nozzles for solution A and a plurality of nozzles forsolution B. Preferably, the nozzles for solution A and that for solutionB are parallel and are arranged with the same intervals, and a mixingand reacting zone is arranged right ahead of the nozzles.

[0069]FIG. 6 shows a coaxial ejection mixing reactor with a side inletfor solution B and a plurality of nozzles for solutions A and C.

[0070] The solutions in the tubular ejection mixing reactor are quicklymixed in a state of micro liquid aggregates by the turbulent function.The mixing and reacting zones are arranged orderly along the flowingdirection of the liquid stream. The tubular ejection mixing reactorshall be operated under a turbulent state in order to high extensivelyand mechanically mix the two solutions. Therefore, the reynolds numbershall be regulated on the basis of the equation of Re=ρVD/μ, wherein, Dis the diameter of the pipe, V is the flow speed of the liquid stream,pis the density of the liquid stream and ρ is the viscosity of theliquid stream. The relationship of the diameter of the pipe, the flowspeed and the flux is shown in the equation of Q=πD²V/4, wherein, Q isthe flux of the liquid stream. As can be seen, once the diameter of thepipe is determined, the flow speed can be determined by the flux of theliquid stream. It shall be further noted that, although the flux of theejected flow is determined by the diameter and the length of theejecting pipe and by the diameter of the large diameter pipe, a pressureis required to maintain the flux of the ejected flow. Therefore, therelated parameters can be concluded as the diameter of a pipe, the flux,the pressure and the reynolds number. The related parameters of thesecond solution and the mixing liquid stream shall also be considered.The inner diameter of the tubular ejection mixing reactor is in therange of 0.5 mm-10 mm. The flux of the ejected flow is in the range of0.1-3000 m³/h, preferably 0.1-800 m³/h. The pressure of the ejected flowis in the range of 30-3000 kg/cm², preferably 50-1000 kg/cm². Thereynolds number Re of the ejected flow is in the range of 2000-20000,preferably 2000-8000. The large diameter pipe of the ejection mixingreactor has a diameter of 5-1000 mm, preferably 5-500 mm. The reynoldsnumbers of the second solution and the mixed flow are in the range of3000-10000, preferably 4000-8000.

[0071]FIG. 7-a shows a tubular static mixing reactor for two reactantsolutions. The reactor comprises (but not limited to) an inlet 1 for onesolution, an inlet 2 for another solution, and mixing units 5-9. Thenumber of the mixing unit is determined based on the specificrequirements. The mixing units of the tubular static mixing reactorcontain some mixing members, for example, Ross mixing member, Sulzermixing member, Kenics mixing member, Etoflo mixing member, see IndustryMixing Process (translated in Chinese), N. Harnby, M. F. Edwards, A. W.Nierow. Beijing, China Petrochemical Publishing House, 1985, Edition 1,p. 279-282. This book is entirely incorporated herein as a reference.The mixing unit further contains a hole/separator mixing member, seeFIG. 8-a, or a grid mixing member, see FIG. 8-b.

[0072] Taking Ross mixing member as an example, the mixing, reaction,formation of the nano-particle and precipitation processes in thetubular static mixng reactor will be illustrated. The structure of Rossmixing member can also be found in Industry Mixing Process (translatedin Chinese), N. Harnby, M. F. Edwards, A. W. Nierow., Beijing, ChinaPetrochemical Publishing House, 1985, Edition 1, p279-282. An ellipsicalplate was cut into two separated parts along its long axis. The twoseparated parts are rotated around the short axis for 900 and used as apair of front separators of the mixing members. The separators arewelded on a support with an angle of 45° between the axis of the largediameter pipe and the plate surface. The mixing member further containsa pair of back separators along the axis of the pipe of the mixingreactor. Except that the back separators are rotated around the axis ofthe pipe of the mixing reactor for 900, the back separators have thesame structure as that of the front separators. The tubular staticmixing reactor can have a series of mixing units comprised of the frontseparators and the back separators. During the mixing of two solutions,the mixing units are static and the energy for mixing comes from theadditional pressure drop created by the passage of the solutions throughthe mixing units. The laminar convection and the turbulent flow bothfacilitate the mixing procedure. The fluid will be separated by theseparators into a plurality of smaller flows and the flow direction willbe changed by the separators, as a result, the laminar convection isformed. The turbulent flow is obtained by controlling the reynoldsnumber. As a result, two solutions are broken and dispersed intoseparated micro liquid aggregates due to impacting, shearing, stretchingand eddying caused by extensively convection and turbulence. The averagesize of the micro liquid aggregate is in relation to the mixingintensity and reynolds number Re, specifically, to the pipe diameter andthe flow speed. The flow speed is in relation to the flux and thepressure. The average size of the micro liquid aggregate can be as smallas tens of microns. As previously stated, a large amount of pristinenuclei will be explosively formed in the vicinity of fresh interfaces ofthe two solutions. The density (number of pristine nuclei per unit ofvolume of the reactor) is relatively high. As shown by experiments, atthis case, the particle size of the nano-particle produced by collisionand aggregation between the pristine nuclei will become smaller and thenano-particles are loosely dispersed in the space of the reactor. Theinner diameter of the tubular static mixing reactor is in the range of 5mm to 1000 mm, preferably 5 mm to 500 mm. The flux of various reactantsolutions is a range of 0.1-3000 m³/h. The inlet pressure of thesolution is 0.5-3000 kg/cm², preferably 2-1000 kg/cm². The reynoldsnumber of the solutions and the mixed flow is in the range of3000-20000, preferably 3000-8000.

[0073]FIG. 7-b and 7-c show a tubular static mixing reactor for three ormore solutions. Besides the members shown in FIG. 7-a, it furthercomprises an inlet 4 for an adjuvant reactant solution C.

[0074] As to the atomization mixing reactor used in the step (b) of thepresent invention, reactant solutions A and B can be sprayed out using afirst and a second atomizer. If required, the atomization mixing reactorcan further contain a third atomizer for adjuvant reactant solution.

[0075]FIG. 9 shows an atomization mixing reactor having two atomizerswhich are especially suitable for the present method. It comprises twoatomizers 1 and 2 capable of forming oriented gas stream, a roller 3, ascraper 4, a funnel 5 and a transfer pump 6. It is operated as follows:(a) reactant solutions A and B are fed into two atomizers 1 and 2 at theinlet of the mixing reactor with two atomizers; (b) the atomized gasstreams from the reactant solutions A and B are atomizing in the samedirection onto the roller 3 or a transfer belt where the atomizeddroplets of the reactant solutions A and B mixes and reacts with eachother to form a precipitate-containing slurry; (c) theprecipitate-containing slurry is transferred by the roller or thetransfer belt to the scraper 4 where it was bladed off, collected to thefunnel 5, and sent to a rinsing and filtering device through a pipe anda pump 6; and (d) the transfer belt comprises a wet filter cloth usedfor a belt-type filter, and the aging time prior to filtering andrinsing is regulated by the filter cloth moving speed v and the lengthΔ1 of the filter cloth prior to reaching the filtering and rinsing zone.The aging time can be calculated according to the equation Δt=Δ1/v. Thefluxes of reactant solutions A and B are in the range of 0.1-3000 m³/h,and the pressures are in the range of 10-3000 kg/cm².

[0076] During the solutions continuously and orderly mixed and reactedwith each other to form a precipitate, from the point of how thesolutions are separated and dispersed into micro liquid aggregates, themethod using an atomization mixing reactor and the method using atubular ejecting (or static) mixing reactor are different.

[0077] In the method using a tubular ejecting (or static) mixingreactor, two solutions are separated and dispersed into separated microliquid aggregates due to impacting, shearing, stretching and eddyingcaused by extensively convection and turbulence. The average size of themicro liquid aggregate is in relation to the mixing intensity andreynolds number Re. However, in the method using an atomization mixingreactor, the two solutions are atomized as two sorts of fine dropletsusing atomizers in air, and the resulting two sorts of fine droplets arealternatively falling on the same position of the roller or the transferbelt. As a result, the two sorts of micro liquid aggregates are mixedwith each other. But from the point of the procedure and the rules ofthe explosive formation of pristine nuclei on the interfaces of themicro liquid aggregates by making two solutions mix and react with eachother, the atomizing mixing and the tubular ejecting (or static) mixingare the same. That is, the smaller the micro liquid aggregates are, thehigher the fresh interface area is, and the higher the total number ofthe pristine nuclei and the average density (number per unit of thespace) are. And if a large amount of pristine nuclei are explosivelyformed and the average density (number per unit of volume of the space)is very high, the particle size of the nano-particle obtained bycollision and aggregation of the pristine nuclei will become smaller.

[0078] Various atomizers can be used in the present method, but amongthem, the following two are preferred.

[0079] a. Pressure Nozzle

[0080] A certain pressure (typically 2-20 MPa, or higher) is provided bya high pressure pump to the solutions. When passing the nozzle, thestatic pressure energy is transferred into dynamic energy and thesolutions are ejected at a high speed and separated into atomizeddroplets. The size of the atomized droplets obviously depends upon thepressure of the liquid stream. This atomizing method is simple,inexpensive and low at energy consumption.

[0081] b. Gas Stream Nozzle

[0082] The solutions are ejected from the nozzles by a pressure gas at ahigh speed (300 m/s or sonic speed) and are separated into atomizeddroplets due to the friction caused by the speed difference between thegas phase and the liquid phase. When the gas is atomized, the pressureof the liquid phase mainly influences the flux but has little influenceon the size of atomized droplets. The pressure of the liquid phase isgenerally not higher than 0.4 MPa, and that of the gas phase isgenerally in the range of 0.3-0.7 MPa. The contacting points of theliquid phase and the gas phase can be in the inner or outer of thenozzles. The atomizing effect is good, the liquid droplets are fine andcan be as small as 50 microns. The size of the liquid droplets dependsupon the gas speed and is in relation to the gas pressure. The energyconsumption of this atomizing method is about several times of that ofthe pressure atomizing method.

[0083] In summary, by the above atomizers, the solutions can be easilyseparated and dispersed into micro liquid aggregates having an averagesize as small as 100 microns or even tens of microns. That is, from thepoint of average size, the property of the atomization mixing reactor isnot inferior to that of the tubular ejecting (or static) mixing reactor.Besides the fluxes of the solutions, the main parameter to be controlledis the size of atomized droplets. The fluxes of the solutions are in therange of 0.1-3000 m³/h, preferably 0.1-800 m³/h. The size of atomizeddroplets is 20-300 microns. In the method using pressure nozzles, thepressure used for the feeding solutions is 20-500 kg/cm², preferably20-300 kg/cm². In the method using gas stream nozzles, the pressure usedfor the feeding solutions is 3-50 kg/cm², preferably 3-20 kg/cm².

[0084] The method of the present invention can be applied to variousreactions capable of reacting rapidly and forming precipitates.Therefore there is no specific limitation on the kinds of precipitatesand formed nano-powders provided by the present invention. For instance,metals (including alloys), oxides, hydroxides, salts, phosphides andsulfides or organic compounds are all in the scope of the presentinvention.

[0085] As compared with the existing technology, the method of thepresent invention has the following advantages:

[0086] (1) particulate diameter of the nano-particles is adjustable, thehomogeneity of the particle size is very good, the dispersity of thenano-particle is good, the hard agglomeration of the nano-particles canbe completely prevented, and thus the quality of the nano-powder isexcellent;

[0087] (2) it can be used to produce a nano-particle loose aggregatepowder comprised of smaller and homogeneous nano-particles and having ahomogeneously distributed and regulable loose degree and porosity and ahigher specific surface area;

[0088] (3) this method can give a high yield and can be used in alarge-scale production;

[0089] (4) as compared with the micro liquid aggregates mixing andreacting precipitator used in Chinese Patent Application No. 01106279.7,the mixing and reacting precipitator where the micro liquid aggregatescan quickly and orderly mix and react with each other has no dynamicrotator, and the controlling of the parameters can be greatlysimplified; and

[0090] (5) the process is simple and low in energy consumption.

[0091] Detailed illustrations of examples of the present invention arefurther given by combining the attached figures. However, these examplesdo not mean any limitation in any form on the scope of the presentinvention.

EXAMPLE 1

[0092] 773.4 g of zirconium oxide chloride ZrOCl_(20.8)H₂O (molecularweight=322.25 and purity ≧99%) was weighed and 3000 ml of 0.8 mol/LZrOCl₂ aqueous solution was prepared from the zirconium oxide chloride,called solution A. Secondly-distillated water and then 2100 ml ofethanol (95%) as a dispersing agent were added to 375 ml of ammoniahaving a NH₃ concentration of 25% to produce 3000 ml of an aqueoussolution called solution B. Solution A and solution B were mixed in atubular coaxial ejection mixing reactor as shown in FIG. 3-a and reactedwith each other to form precipitate at room temperature of 20° C. asillustrated in the process flow chart shown in FIG. 2. The pH value ofthe resultant was adjusted to be 7-8 by the addition of ammonia. Thetubular coaxial ejection mixing reactor had an inner diameter of 10 mmand an inner diameter of spray hole of 1 mm. The flows of solution A andsolution B are both 200 L/h. The pressure at the spray inlet forsolution A was 100 kg/cm². The slurry containing the resultingprecipitate was fed into a continuously-running equipment for rinsingand filtration, then subject to azeotropic distillation in the presenceof n-butanol and dried, and sintered at the temperature of 650° C. for50 min to obtain Zro₂ nano-powders having an average particle diameterof 15 nm and having good uniformity in particle diameter and goodparticle dispersibility. The yield of Zro₂ was 92%.

EXAMPLE 2

[0093] 333.6 g of ZnCl₂ was weighed and secondly-distillated water wasadded to produce 3000 ml of 0.8 mol/L ZnCl₂ aqueous solution calledsolution A at a temperature of 70° C. 900 ml ethanol (95%) as adispersing agent was added to 375 ml of ammonia water (25%) to produce3000 ml of 0.8 mol/L NH₃ aqueous solution in ethanol called solution Bat a temperature of 30° C. Solution A and solution B were mixed in atubular coaxial ejection mixing reactor as shown in FIG. 3-a and reactedwith each other to form precipitate as illustrated in the process flowchart shown in FIG. 2. The pH value of the resultant was adjusted to be7-8 by the addition of ammonia. The tubular coaxial ejection mixingreactor had an inner diameter of 10 mm and an inner diameter of sprayhole of 1 mm. The flows of solution A and solution B are both 150 L/h.The pressure at the spray inlet for solution A was 90 kg/cm². The slurrycontaining the resulting precipitate was fed into a continuously-runningequipment for rinsing and filtration, then subject to azeotropicdistillation in the presence of n-butanol and dried, and sintered at thetemperature of 550° C. for 30 min to obtain ZnO nano-powders having anaverage particle diameter of 40 nm and having good uniformity inparticle diameter and good particle dispersibility. The yield of ZnO was92%.

EXAMPLE 3

[0094] 441.6 g of BaCI₂ was weighed and secondly-distillated water and900 ml ethanol were added to produce 3000 ml of 0.6 mol/L BaCl₂ aqueoussolution called solution A at a temperature of 20° C. 156.6 g of NH₄HCO₃was weighed and secondly-distillated water, 180 ml of ammonia water(25%) and 1200 ml of ethanol (95%) as a dispersing agent were added toproduce a 3000 ml solution called solution B at a temperature of 20° C.Solution A and solution B were mixed in a tubular coaxial ejectionmixing reactor as shown in FIG. 3-a and reacted with each other to formprecipitate as illustrated in the process flow chart shown in FIG. 2.The pH value of the resultant was adjusted to be 7-8 by the addition ofammonia water. The tubular coaxial ejection mixing reactor had an innerdiameter of 10 mm and an inner diameter of spray hole of 1 mm. The flowsof solution A and solution B are both 160 L/h. The pressure at the sprayinlet for solution A was 100 kg/cm². The slurry containing the resultingprecipitate was fed into a continuously-running equipment for rinsingand filtration, then subject to azeotropic distillation in the presenceof n-butanol and dried, and sintered at the temperature of 550° C. for45 min to obtain columnar crystalline BaCO₃ nano-powders having adiameter of 30 nm and length of 90 nm and having good uniformity inparticle diameter and good particle dispersibility. The yield of BaCO₃was 93%.

EXAMPLE 4

[0095] 1289 g of zirconium oxide chloride ZrOCl_(20.8)H₂O (molecularweight=322.25 and purity ≧99%) was weighed and 5000 ml of 0.8 mol/LZrOCl₂ aqueous solution was prepared from the zirconium oxide chloride,called solution A. Secondly-distillated water and then 1750 ml ofethanol (95%) as a dispersing agent were added to 625 ml of ammoniawater having a NH₃ concentration of 25% to produce 5000 ml of an aqueoussolution called solution B. Solution A and solution B were mixed in atubular static mixing reactor as shown in FIG. 7-a and reacted with eachother to form precipitate at room temperature of 20° C. as illustratedin the process flow chart shown in FIG. 2. The pH value of the resultantwas adjusted to be 7-8 by the addition of ammonia. The tubular staticmixing reactor had an inner diameter of 10 mm and was provided insidewith a Ross mixing member. The flows of solution A and solution B areboth 600 L/h. The pressure at the spray inlet for solution A was 4kg/cm². The slurry containing the resulting precipitate was fed into acontinuously-running equipment for rinsing and filtration, then subjectto azeotropic distillation in the presence of n-butanol and dried, andsintered at the temperature of 620° C. for 45 min to obtain ZrO₂nano-powders having an average particle diameter of 16 nm and havinggood uniformity in particle diameter and good particle dispersibility.The yield of Zro₂ was 91%.

EXAMPLE 5

[0096] 556 g of ZnCl₂ was weighed and secondly-distillated water wasadded to produce 5000 ml of 0.8 mol/L ZnCl₂ aqueous solution calledsolution A at a temperature of 70° C. 1500 ml ethanol (95%) as adispersing agent was added to 625 ml of ammonia water (25%) to produce5000 ml of 0.8 mol/L NH₃ aqueous solution in ethanol called solution Bat a temperature of 30° C. Solution A and solution B were mixed in atubular coaxial ejection mixing reactor as shown in FIG. 7-a and reactedwith each other to form precipitate as illustrated in the process flowchart shown in FIG. 2. The pH value of the resultant was adjusted to be7-8 by the addition of ammonia. The tubular static mixing reactor had aninner diameter of 10 mm and was provided inside with a Ross mixingmember. The flows of solution A and solution B are both 500 L/h. Thepressures at the spray inlets for solutions were both 3.5 kg/cm². Theslurry containing the resulting precipitate was fed into acontinuously-running equipment for rinsing and filtration, then subjectto azeotropic distillation in the presence of n-butanol and dried, andsintered at the temperature of 530° C. for 35 min to obtain ZnOnano-powders having an average particle diameter of 35 nm and havinggood uniformity in particle diameter and good particle dispersibility.The yield of ZnO was 93%.

EXAMPLE 6

[0097] 736 g of BaCl₂ was weighed and secondly-distillated water and1500 ml ethanol were added to produce 5000 ml of 0.6 mol/L BaCl₂ aqueoussolution called solution A at a temperature of 20° C. 261 g of NH₄HCO₃was weighed and secondly-distillated water, 300 ml of ammonia water(25%) and 2000 ml of ethanol (95%) as a dispersing agent were added toproduce a 5000 ml solution called solution B at a temperature of 20° C.Solution A and solution B were mixed in a tubular static mixing reactoras shown in FIG. 7-a and reacted with each other to form precipitate asillustrated in the process flow chart shown in FIG. 2. The pH value ofthe resultant was adjusted to be 7-8 by the addition of ammonia water.The tubular static mixing reactor had an inner diameter of 10 mm and wasprovided inside with a Ross mixing member. The flows of solution A andsolution B are both 550 L/h. The pressures at the spray inlets forsolutions were both 3.8 kg/cm². The slurry containing the resultingprecipitate was fed into a continuously-running equipment for rinsingand filtration, then subject to azeotropic distillation in the presenceof n-butanol and dried, and sintered at the temperature of 530° C. for35 min to obtain columnar crystalline BaCO₃ nano-powders having adiameter of 35 nm and length of 80 nm and having good uniformity inparticle diameter and good particle dispersibility. The yield of BaCO₃was 86%.

EXAMPLE 7

[0098] 515.6 g of zirconium oxide chloride ZrOCl_(20.8)H₂O (molecularweight=322.25 and purity ≧99%) was weighed and 2000 ml of 0.8 mol/LZrOCl₂ aqueous solution was prepared from the zirconium oxide chloride,called solution A. Secondly-distillated water and then 700 ml of ethanol(95%) as a dispersing agent were added to 250 ml of ammonia having a NH₃concentration of 25% to produce 2000 ml of an aqueous solution calledsolution B. Solution A and solution B were mixed in a atomization mixingreactor with two atomizers as shown in FIG. 9 and reacted with eachother to form precipitate at room temperature of 20° C. as illustratedin the process flow chart shown in FIG. 2. The pH value of the resultantwas adjusted to be 7-8 by the addition of ammonia. The atomizationmixing reactor with two atomizers was provided with a pressure nozzlewith a spray pressure of 160 kg/cm². The flows of solution A andsolution B are both 200 L/h. The two reactant solutions were formed intoatomized gas streams in the same one direction and sprayed to the wallof the roll, where the two reactant solutions were mixed and reacted toform precipitate. The precipitate-containing slurry was collected andfed into a continuously-running equipment for rinsing and filtration,then subject to azeotropic distillation in the presence of n-butanol anddried, and sintered at the temperature of 650° C. for 30 min to obtainZrO₂ nano-powders having an average particle diameter of 18 nm andhaving good uniformity in particle diameter and good particledispersibility. The yield of ZrO₂ was 94%.

EXAMPLE 8

[0099] 222.5 g of ZnCl₂ was weighed and secondly-distillated water wasadded to produce 2000 ml of 0.8 mol/L ZnCl₂ aqueous solution calledsolution A at a temperature of 70° C. 600 ml ethanol (95%) as adispersing agent was added to 250 ml of ammonia water (25%) to produce2000 ml of 0.8 mol/L NH₃ aqueous solution in ethanol called solution Bat a temperature of 30° C. Solution A and solution B were mixed in aatomization mixing reactor with two atomizers as shown in FIG. 9 andreacted with each other to form precipitate at room temperature of 20°C. as illustrated in the process flow chart shown in FIG. 2. The pHvalue of the resultant was adjusted to be 7-8 by the addition ofammonia. The atomization mixing reactor with two atomizers was providedwith a pressure nozzle with a spray pressure of 160 kg/cm². The flows ofsolution A and solution B are both 200 L/h. The two reactant solutionswere formed into atomized gas streams in the same one direction andsprayed to the wall of the roll, where the two reactant solutions weremixed and reacted to form precipitate. The precipitate-containing slurrywas collected and fed into a continuously-running equipment for rinsingand filtration, then subject to azeotropic distillation in the presenceof n-butanol and dried, and sintered at the temperature of 520° C. for35 min to obtain ZnO nano-powders having an average particle diameter of36 nm and having good uniformity in particle diameter and good particledispersibility. The yield of ZnO was 95%.

EXAMPLE 9

[0100] 294.4 g of BaCl₂ was weighed and secondly-distillated water and600 ml ethanol were added to produce 2000 ml of 0.6 mol/L BaCl₂ aqueoussolution called solution A at a temperature of 20° C. 104.4 g of NH₄HCO₃was weighed and secondly-distillated water, 120 ml of ammonia water(25%) and 800 ml of ethanol (95%) as a dispersing agent were added toproduce a 2000 ml solution called solution B at a temperature of 20° C.Solution A and solution B were mixed in a atomization mixing reactorwith two atomizers as shown in FIG. 9 and reacted with each other toform precipitate as illustrated in the process flow chart shown in FIG.2. The pH value of the resultant was adjusted to be 7-8 by the additionof ammonia. The atomization mixing reactor with two atomizers wasprovided with a pressure nozzle with a spray pressure of 200 kg/cm². Theflows of solution A and solution B are both 200 L/h. The pressures atthe spray inlets for solutions were both 3.8 kg/cm². The slurrycontaining the resulting precipitate was fed into a continuously-runningequipment for rinsing and filtration, then subject to azeotropicdistillation in the presence of n-butanol and dried, and sintered at thetemperature of 530° C. for 40 min to obtain columnar crystalline BaCO₃nano-powders having a diameter of 32 nm and length of 89 nm and havinggood uniformity in particle diameter and good particle dispersibility.The yield of BaCO₃ was 86%.

1. A process for preparing nano-powders and nano-particle looseaggregate powders, comprising the steps of: (a) providing at least tworeactant solutions A and B which can react with each other quickly toform precipitate; (b) feeding the at least two reactant solutions A andB to a mixing and reaction precipitator separately which is at least oneselected from a group consisting of tubular ejection mixing reactor,tubular static mixing reactor and atomization mixing reactor at atemperature not lower than the reaction temperature for continuous andorderly mixing, reaction and precipitation, where the at least tworeactant solutions A and B react with each other in a form ofmicro-liquid aggregate and form a precipitate-containing slurry; (c)post-treating the precipitate-containing slurry discharged continuouslyand orderly from the reaction precipitator.
 2. The process according toclaim 1, wherein in step (a), at least one of said at least two reactantsolutions further comprises an adjuvant reactant and/or a dispersingagent.
 3. The process according to claim 1, wherein in step (a), one ormore adjuvant reactant solutions comprising at least one selected from agroup consisting of a dispersing agent, an adjuvant reactant and a pHadjuster.
 4. The process according to claim 1, wherein in step (a), saidtwo reactant solutions A and B are each independently aqueous solutionsor organic solutions.
 5. The process according to claim 4, wherein saidaqueous solutions or organic solutions are at a temperature from 15° C.to the boiling point of the solutions.
 6. The process according to claim1, wherein in step (b), said reactant solutions are rapidly dispersedand pulverized to micro-liquid aggregates in finely divided form in themixing and reaction precipitator.
 7. The process according to claim 1,wherein the residence time of said reactant solutions in said mixingreactor is from 0.1 second to 120 seconds.
 8. The process according toclaim 7, wherein the residence time of said reactant solutions in saidmixing reactor is from 0.1 second to 10 seconds.
 9. The processaccording to claim 1, wherein in step (b), said tubular ejection mixingand reacting precipitator comprises an inlet for ejecting the reactantsolution A, an inlet for the reactant solution B and a mixing andreaction zone, where said reactant solutions A and B are rapidlydispersed and pulverized to micro-liquid aggregates in finely dividedform with intense turbulent flow and then react with each other to formprecipitate.
 10. The process according to claim 9, wherein said tubularejection mixing and reacting precipitator is selected from a groupconsisting of a coaxial ejection mixing and reacting precipitator, anejection mixing reactor having a side inlet and a multi-nozzle ejectionmixing reactor.
 11. The process according to claim 9, wherein the innerdiameter of the hole for ejecting is from 0.5 mm to 10 mm.
 12. Theprocess according to claim 9, wherein the flux of the ejected liquid is0.1-3000 m³/h.
 13. The process according to claim 9, wherein thepressure of the ejected liquid is 30-3000 kg/cm².
 14. The processaccording to claim 9, wherein Re of the ejected liquid is 2000-20000.15. The process according to claim 9, wherein the diameter of the largediameter pipe in said tubular ejection mixing reactor is 5-1000 mm. 16.The process according to claim 9, wherein Re of the second reactionliquid stream and mixing liquid stream is 3000-10000.
 17. The processaccording to claim 1, wherein a mixing member capable of rapidlydispersing and pulverizing the reactant solutions to micro-liquidaggregates in finely divided form is provided in said tubular staticmixing and reaction precipitator in step (b).
 18. The process accordingto claim 17, wherein said mixing member is one or more selected from agroup consisting of Ross mixing members, Sulzer mixing members, Kenicsmixing members, hole-separator type mixing members and grid mixingmembers.
 19. The process according to claim 17, wherein the innerdiameter of the pipes in said tubular static mixing reactor is from 5 mmto 1,000 mm.
 20. The process according to claim 17, wherein the flux ofeach of the reactant solutions is in the range of 0.1-3,000 m³/h. 21.The process according to claim 17, wherein the inlet pressure of thesolutions is 0.5-3,000 kg/cm².
 22. The process according to claim 17,wherein Re of the reactant solution stream and mixing liquid stream is3,000-20,000.
 23. The process according to claim 1, wherein saidatomization mixing and reaction precipitator comprises: (a) at least onefirst atomizer capable of making a reactant solution to an orientedatomized gas stream; (b) at least one second atomizer capable of makingat least one of the remaining reactant solutions to an oriented atomizedgas stream; and (c) a roller or transfer belt carrying and transferringthe reaction precipitate for the intersection and overlapping ofdifferent liquid micro-liquid droplets at the same one  region so as toachieve the mixing of micro-liquid aggregates with each other; andwherein said first atomizer and said second atomizer spray the reactantsolutions separately onto the roller or transfer belt in one direction.24. The process according to claim 23, wherein the size of the sprayeddroplets is 20-300 μm.
 25. The process according to claim 23, whereinthe flows of the reactant solutions A and B are independently 0.1-3,000m³/h.
 26. The process according to claim 18, wherein the pressure of theliquid stream is 20-500 kg/cm², when said atomizer is a pressure nozzle.27. The process according to claim 18, wherein the pressure of thepressured gas is 3-50 kg/cm², when said atomizer is a gas stream nozzle.28. The process according to claim 23, wherein said atomization mixingand reaction precipitator further comprises a third atomizer capable ofmaking said adjuvant reactant solution to an oriented atomized gasstream.
 29. The process according to claim 23, wherein a filter deviceis provided on said transfer belt.
 30. The process according to claim23, wherein said filter device is a wet filter cloth.
 31. The processaccording to claim 23, further comprising a step of collecting theprecipitate-containing slurry from said roller or transfer belt and thenpost-treating the same.
 32. The process according to claim 1, wherein instep (c), said precipitate-containing slurry is post treated immediatelyafter continuously discharged from said mixing and reactionprecipitator.
 33. The process according to claim 1, wherein the processsteps in said step (c) comprise separation, drying and pulverization.34. The process according to claim 33, wherein said separation stepcomprises rinsing and filtering, preferably conducted in a continuousequipment.
 35. The process according to claim 33, wherein said dryingstep further comprises azeotropic distillation.
 36. The processaccording to claim 1, wherein in said step (c), saidprecipitate-containing slurry is firstly subject to aging and then otherpost treatment after discharged continuously from the mixing andreaction precipitator to produce nano-particle loose aggregate powder.37. The process according to claim 1, wherein said nano-powders andnano-particle loose aggregate powders are one or more selected from agroup consisting of metals, oxides, hydroxides, salts, phosphides andsulfides, or organic compounds.
 38. The process of claim 12, wherein theflux of the ejected liquid is 0.1-800 m³/h.
 39. The process according toclaim 13, wherein the pressure of the ejected liquid is 50-1,000 kg/cm².40. The process according to claim 14, wherein Re of the ejected liquidis 2,000-8,000.
 41. The process according to claim 15, wherein thediameter of the large diameter pipe in said tubular ejection mixingreactor is 5-500 mm.
 42. The process according to claim 16, wherein Reof the second reaction liquid stream and mixing liquid stream is4,000-8,000.
 43. The process according to claim 19, wherein the innerdiameter of the pipes in said tubular static mixing reactor is from 5 mmto 500 mm.
 44. The process according to claim 21, wherein the inletpressure of the solutions is 2-1,000 kg/cm².
 45. The process accordingto claim 22, wherein Re of the reactant solution stream and mixingliquid stream is 3,000-8,000.
 46. The process according to claim 25,wherein the flows of the reactant solutions A and B are independently0.1-800 m³/h.
 47. The process according to claim 26, wherein thepressure of the liquid stream is 20-300 kg/cm², when said atomizer is apressure nozzle.
 48. The process according to claim 27, wherein thepressure of the pressured gas is 3-20 kg/cm², when said atomizer is agas stream nozzle.